HALSacc                 Accelerated hierarchical alternating least
                        squares NMF. For a reference to the method, see
                        N. Gillis, Nonnegative matrix factorization:
                        complexity, algorithms and applications
                        [Section 4.2, Algo. 6], PhD thesis, Universit
                        catholique de Louvain, February 2011.
PGNMF                   NMF by alternating non-negative least squares
                        using projected gradients.  For a reference to
                        the method, see C.-J. Lin, "Projected Gradient
                        Methods for Non-negative Matrix Factorization",
                        Neural computation 19.10 (2007): 2756-2779.
hNMF                    Hierarchical non-negative matrix factorization.
imoverlay               Overlay a mask or a color scaled image on top
                        of a background image
initializeNMF           Initialize NMF model with initial spectral data
initializeSPA           The successive projection algorithm, a useful
                        method for initializing the NMF source matrix
oneLevelNMF             Perform Non-Negative Matrix factorization
preProcesInputData      Condition input data matrix properly for NMF
scaleNMFResult          Apply fixed scaling to NMF model matrices by
                        normalizing the basis vectors
semiNMF                 Semi-NMF based on multiplicative update rules.
                        Reference: C. Ding, T. Li, and M.I. Jordan,
                        "Convex and semi-nonnegative matrix
                        factorizations", IEEE Transations on Pattern
                        Analysis and Machine Intelligence, vol. 32, no.
                        1, pp. 45-55, 2010.
